Handwriting

3 ) Why did Leonardo write in way that could only be decoded from a mirror?

In an era when left-handedness was considered the devil's work and lefties were often forced to use their right hand, Leonardo was an unrepentant southpaw. It has been suggested that this "difference" was an element of his genius, since his detachment allowed him to see beyond the ordinary. He even wrote backwards, and his writings are easily deciphered only with a mirror. This was probably also to keep his notes a secret.